The problem of provision of a strong leak-proof joint between tubular or cylindrical members has been of interest for many years. There are numerous features which are desirable in such a clamp, in addition to the obvious requirements that the joint be leak-proof and durable in service. A satisfactory clamp must also be simple of installation, inexpensive to manufacture, provide structural strength to the joint, particularly to butt joints, in which the ends of the cylindrical members abut one another rather than one telescoping inside another, as in a lap joint configuration, and must be capable of installation in a "band-aid" fashion, that is, without separating the two tubes from one another.
The prior art shows numerous attempts to achieve all these goals. See, for example, U.S. Pat. Nos. 3,905,623 and 4,261,600 to Cassel in both of which the ends of the band are contacted by opposed shaped clamping members disposed on opposite sides of a channel formed in the band. A central shaping member is disposed within the channel, so that upon tightening of bolts extending through the two outer shaping members, the channel formed by the band and the inner shaping member, the metal of the band is deformed and constrained to stretch into close contact with the shaping members, thus tightening the band around the tube. However, these clamps suffer from the distinct disadvantage that they are difficult to assemble in the field, as they require numerous parts to be lined up with one another so that the bolts can be thrust through corresponding holes. Furthermore, provision of the plural shaping members is costly. A somewhat similar design with some of the same disadvantages is shown in commonly assigned copending application, Ser. No. 205,639 filed Nov. 10, 1980, now U.S. Pat. No. 4,364,588, and another similar approach is shown in U.S. Pat. No. 4,165,109 to Foti.
A somewhat different approach is shown in U.S. Pat. No. 4,142,743 to McGowan et al. There a flat band of metal having flat clamping bars welded to its ends is assembled around the tube. The spacing of the holes in the ends of the band with respect to the diameter of the tube is such that the clamping bars do not meet until the bolts are tightened, thus causing the band to be stretched into conformity with the outer surfaces of the tubes to be coupled. This clamp is not without utility, but it is sometimes difficult to assemble due to the close fit of the bolts within their holes necessary in order to insure proper assembly. A somewhat similar approach is shown also in U.S. Pat. No. 3,944,265 to Hiemstra et al, reissued as U.S. Pat. No. Re. 30,042. Both the Hiemstra et al patents and the McGowan patent suffer from the deficiency that the spacing of the holes in the end of the band must be very carefully controlled in order that the clamping bars can meet one another squarely and completely upon tightening of the clamp without overtightening of the bolts or undertensioning of the band, which is important in order that a strong and rigid joint can be made. Stated somewhat differently, in order that a strong and rigid joint can be formed, it is essential that a substantially uniform compressional force be exerted all the way around the joint. According to the Heimstra and McGowan designs, this is only possible when the two clamping bars are pulled up close together by the tightening of the bolts. This can only occur when the hole spacing and the pipe sizes are very closely controlled with respect to one another. Otherwise, in the case where the tube is comparatively too large for the bolt hole spacing in the band, the bars will not meet, causing leakage, while if the band hole spacing is too great, the faces of the clamping bars will meet without sufficient stress being exerted on the band, thus resulting in a leaky joint. McGowan et al and Hiemstra et al both recognize this problem and provide a separate compressible, resilient sealing member to prevent leakage in the vicinity of the joint.
Accordingly, there remains a need of the industry for an improved band seal clamp.